(1) Field of the Invention
The present invention relates to an image synthesizing apparatus which, having been inputted with plural images of differing spatial resolution (hereafter, referred to simply as “resolution”) resulting from differences in enlargement ratios and so on at the time of capturing the images, generates a synthesized image of a higher resolution, and particularly relates to a technique for improving the resolution of an image using plural images between which exist differences in resolution and lighting conditions.
(2) Description of the Related Art
As an image synthesizing apparatus which synthesizes high-resolution images using conventional image processing technology, there exists an image synthesizing apparatus which, upon being provided with an original image, improves the resolution of the original image by superimposing, onto the original image, a high-resolution reference image in which the same object has been captured.
As a specific example of such an image synthesizing apparatus, Patent Reference 1 (Japanese Laid-Open Patent Application No. 2003-203237) discloses an image synthesizing apparatus which takes a low-resolution image and a high-resolution image in which the same object has been captured at short and long cycles respectively and performs a two-dimensional geometric conversion on the high-resolution image, thereby generating a high-resolution synthesized image which has the same composition as that of the low-resolution image.
Furthermore, as another image synthesizing apparatus, which generates a synthesized image with arbitrary lighting conditions from plural images with differing lighting conditions using conventional image processing technology, there exists an image synthesizing apparatus which generates a synthesized image with arbitrary lighting conditions using image linearization. “Images with differing lighting conditions” refers to images captured in situations where the position and distance of the light source from the object, the shape and number of light sources, and so on differ from image to image.
As a specific example of this type of image synthesizing apparatus, Patent Reference 2 (Japanese Laid-Open Patent Application No. 2004-5509) discloses an image synthesizing apparatus which uses plural images in which the face of the same person is captured at different angles and coordinate values of corresponding points between the images to generate an image having different lighting conditions relative to a certain angle. FIG. 1 shows examples of synthesized images generated by the conventional image synthesizing apparatus described in the aforementioned Patent Reference 2; synthesized images with differing angles and lighting conditions can be generated thereby.